Coherent self-homodyne detection (SHD) was originally proposed in the following Non-Patent Literature 1 [T. Miyazaki and F. Kubota, “PSK self-homodyne detection using a pilot carrier for multibit/symbol transmission with inverse-RZ signal, Photonics Technology Letters, Vol. 17, No. 6, June 2005] and consists in sharing the light from a light source into two orthogonal polarization components. One of these components is modulated with a coherent information signal whereas the other remains unmodulated.
Both components are then polarization multiplexed and transmitted through an optical fiber. It has been demonstrated that both components remain phase coherent, event after long transmission distances (Non-Patent Literature 2 [R. Luis, et al., “Digital self-homodyne detection”, submitted to Photonics Technology Letters, November 2014]). At the receiver, a polarization beam splitter separates both components again, sending them to a coherent receiver. There, the polarization of the modulated component is aligned to the polarization axis of the unmodulated component or vice-versa and both components are mixed. The resulting interference signal is converted to the electrical domain by photo-detectors. Since both components are phase coherent, the electrical signal is only modestly affected by phase noise from the transmission light source. Therefore, low-cost wide-linewidth light sources can be used. These receivers are homodyne and therefore, do not require carrier frequency offset estimation or compensation. In addition, they do not require the use of a potentially costly laser to be used as local oscillator at the receiver. For this reason, they have been recently proposed for use in cost-sensitive applications, such as passive optical networks (Non-Patent Literature 3 [R. Luis, et al., “Ultra high capacity self-homodyne PON with simplified ONU and burst-mode upstream”, Photonics Technology Letters, Vol 26, No. 7, April 2014]).